Q:
Hard throttle bucking

asked by
Joe M
on
October 03, 2016

only just bought car ,intermitant fault ,after full service noticed this fault ,split seal on air intake ,replaced ,code stored that keeps apearing ,o2 sensor open circuit ,and exhaust back pressure ,the o2 code clears which leads me to think its not wiring but breaking down internaly ,could this cause surge or kangarooing effect _heavy throttle .car runs well most of the time ,but using more fuel .

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If the split seal on the air intake is after the MAF (Mass Airflow Sensor), it will cause this problem. When you give the motor a lot of throttle, a much larger amount begins to flow into the motor. This rush of air makes the split in the air intake larger pulling in what is known as unmetered air. This means the motor is getting air that the PCM (Powertrain Control Module) does not see entering the motor. The result of this is an incorrect air fuel ratio. Your O2 sensor will detect a problem with the air fuel ratio and set a code.

Following "split seal on air intake", it says replaced. If the air intake has been replaced and these codes are still present, I would turn my attention to the exhaust back pressure code. This would indicate a clogged exhaust. This is fairly easy to check for. Simply attempt to rev the motor in neutral. Floor the gas pedal and see if the motor will quickly move to red line. I know this sounds like a bad thing to do, but I assure you, this is actually a normal test procedure. If it reaches the red line quickly, let off the throttle. If the exhaust is indeed plugged, the RPM (revolutions per minute) will climb slowly and may not actually reach the red line.

Another test is to put your hand in front of the exhaust pipe and see if there is a steady and firm pressure exiting the exhaust pipe. If it is really soft and won’t move your hand, you have a plugged exhaust. To further test this, you can have someone rev the motor while your hand is in front of the exhaust pipe. The pressure should become very strong. If it doesn’t, increase dramatically, you have a plugged exhaust. This is almost always because of a collapsed catalytic converter. A plugged exhaust can create the surging as the catalytic converter can expand and contract varying the amount of air that is allows to pass through the system. Different driving conditions can change this greatly.

Your O2 can have an intermittent open in the O2 circuit. This can happen internally in the O2 or externally in another part of the circuit. It should be noted, if the exhaust is plugged, it can create symptoms such as this.

If you should need further assistance, consider YourMechanic, as one of our mobile technicians can come to you and diagnose the throttle bucking you’re experiencing and help you fix it accordingly.

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